Don't require parentheses around via type (`-XDerivingVia'). Fixes #18130".

6 files changed, 48 insertions, 2 deletions

diff --git a/compiler/GHC/Parser.y b/compiler/GHC/Parser.y
index bafed741be..7c0790da12 100644
--- a/compiler/GHC/Parser.y
+++ b/compiler/GHC/Parser.y
@@ -1209,8 +1209,8 @@ deriv_strategy_no_via :: { LDerivStrategy GhcPs }
                                        [mj AnnNewtype $1] }
 
 deriv_strategy_via :: { LDerivStrategy GhcPs }
-  : 'via' type              {% ams (sLL $1 $> (ViaStrategy (mkLHsSigType $2)))
-                                            [mj AnnVia $1] }
+  : 'via' ktype             {% ams (sLL $1 $> (ViaStrategy (mkLHsSigType $2)))
+                                       [mj AnnVia $1] }
 
 deriv_standalone_strategy :: { Maybe (LDerivStrategy GhcPs) }
   : 'stock'                     {% ajs (sL1 $1 StockStrategy)
diff --git a/testsuite/tests/parser/should_compile/T18130.hs b/testsuite/tests/parser/should_compile/T18130.hs
new file mode 100644
index 0000000000..a796de7a39
--- /dev/null
+++ b/testsuite/tests/parser/should_compile/T18130.hs
@@ -0,0 +1,20 @@
+{-# Language DerivingVia #-}
+{-# Language KindSignatures #-}
+
+module T18130 where
+
+import Data.Functor.Classes
+import Data.Kind
+
+newtype Par a b = Par (a, b)
+  deriving Eq
+  via (a, b)
+   :: Type
+
+  deriving Eq1
+  via (,) a
+   :: Type -> Type
+
+  deriving Eq2
+  via (,)
+   :: Type -> Type -> Type
diff --git a/testsuite/tests/parser/should_compile/all.T b/testsuite/tests/parser/should_compile/all.T
index 1568a341ec..8c7f058062 100644
--- a/testsuite/tests/parser/should_compile/all.T
+++ b/testsuite/tests/parser/should_compile/all.T
@@ -166,3 +166,4 @@ test('proposal-229f',
      multimod_compile_and_run, ['proposal-229f.hs', ''])
 
 test('T15730a', normal, compile_and_run, [''])
+test('T18130', normal, compile, [''])
diff --git a/testsuite/tests/parser/should_fail/T18130Fail.hs b/testsuite/tests/parser/should_fail/T18130Fail.hs
new file mode 100644
index 0000000000..dfd1389b80
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/T18130Fail.hs
@@ -0,0 +1,20 @@
+{-# Language DerivingVia #-}
+{-# Language KindSignatures #-}
+
+module T18130Fail where
+
+import Data.Functor.Classes
+import Data.Kind
+
+newtype Par a b = Par (a, b)
+  deriving Eq
+  via (a, b)
+   :: Type -> Type
+
+  deriving Eq1
+  via (,) a
+   :: Type -> Type
+
+  deriving Eq2
+  via (,)
+   :: Type -> Type -> Type
diff --git a/testsuite/tests/parser/should_fail/T18130Fail.stderr b/testsuite/tests/parser/should_fail/T18130Fail.stderr
new file mode 100644
index 0000000000..60887b0799
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/T18130Fail.stderr
@@ -0,0 +1,4 @@
+
+T18130Fail.hs:11:7: error:
+    • Expected kind ‘* -> *’, but ‘(a, b)’ has kind ‘*’
+    • In the newtype declaration for ‘Par’
diff --git a/testsuite/tests/parser/should_fail/all.T b/testsuite/tests/parser/should_fail/all.T
index c6d691bed3..9d71019f3e 100644
--- a/testsuite/tests/parser/should_fail/all.T
+++ b/testsuite/tests/parser/should_fail/all.T
@@ -166,3 +166,4 @@ test('T17162', normal, compile_fail, [''])
 test('proposal-229c', normal, compile_fail, [''])
 test('T15730', normal, compile_fail, [''])
 test('T15730b', normal, compile_fail, [''])
+test('T18130Fail', normal, compile_fail, [''])